So I found that Cocosbuilder assumes a default CCLayerColor opacity of 255, but Cocos2dx defaults to 0. This causes CCLayerColors created in Cocosbuilder to not display if they have a opacity of 255. I fixed this by changing the following in CCLayerColor::init():

Thank you very much for sharing this bug! It saved me a lot of time!
If you are planning to use CCLayerGradient you should implement a constructor
just to clean the member variables inside it, otherwise you get extrange results be aware